Electric discharge device



P 1965 5. J. CHERRY 3,206,636

ELECTRIC DISCHARGE DEVICE Filed April 28. 1961 CONTROL 24 Sou TROL TAGE SOURCE Fig. 2

WITNESSES iNVENTOR Sidney J. Cherry ATTORN United States Patent 3,206,636 ELECTRIC DISCHARGE DEVICE Sidney J. Cherry, Elmira, N.Y., assiguor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 28, 1961, Ser. No. 106,223 5 Claims. (Cl. 31556) This invention relates to an electric discharge device and more particularly to a cold cathode electric discharge device.

The conventional gas filled cold cathode tube has an anode, cathode, trigger, and usually a priming mechanism. The voltage at which a discharge will occur between the cathode and anode is dependent, in part, upon the state of ionization of the gas within the tube. It only natural causes, such as cosmic rays, are depended upon to furnish initial ionization in the tube, the discharge initiation period is sometimes erratic and long, sometimes as long as one minute. It is, therefore, normal to use a priming mechanism within the tube to insure that charged particles are available to stabilize and accelerate the initial breakdown period.

It is, accordingly, an object of this invention to provide cold cathode discharge tube with a novel electrode structure for initiating discharge in the tube.

Another object of the invention is the provision of a cold cathode discharge tube with a novel cold cathode element which functions both as a cold cathode and as the control element for initiating discharge in the tube.

Another object of the invention is the provision of a cold cathode discharge tube with an improved triggering means which provides for accurate and quick triggering of the tube.

It is another object to provide a cold cathode discharge device having a triggering electrode which is not dependent upon thermionic emission.

The above and other objects are effected by the invention as will be apparent from the following description taken in accordance with the accompanying drawings throughout which like reference characters indicate like parts and in which:

FIGURE 1 is a schematic drawing of a discharge tube incorporating the invention;

FIG. 2 is an enlarged view of the trigger electrode shown in FIG. 1;

FIG. 3 is an illustration of a modification of the discharge device in accordance with the teachings of the invention; and,

FIG. 4 is a top plan view of the modification of FIG. 3 taken substantially along line IV-IV of FIG. 3.

In accordance with the invention, the cold cathode discharge tube is provided With an improved triggering means which functions to control the initiation of the discharge of the tube. Referring to FIG. 1 in detail, there is shown an electron device, more specifically a gaseous discharge device, incorporating a special electrode in accordance with the teachings of the invention. The device includes a hermetically sealed container or envelope 10 which may be of any suitable material, such as glass. This envelope contains a suitable ionizable gas which may be, for example, argon at a pressure of about 15 millimeters of mercury or a mixture of gases such as 99 percent neon and 1 percent argon at a pressure of about 65 millimeters of mercury.

An anode or electron collecting electrode 13 is positioned and sealed within the envelope 10 and is supplied with a suitable positive voltage, for example about volts by means of battery 39, through the lead wire 15. The anode 13 may take the form of a short metal rod and is made of some suitable material such as nickel.

A cathode or electron emissive source 17, which may be of molybdenum although it is noted that other materials such as nickel, tantalum, or columbium may be used, is supported within the envelope by rigid supports 19 which are sealed through the bottom wall or base of the envelope 10. The cathode 17 is connected to ground by means of a lead 11. The cathode 17 and anode 13 are positioned within the tube and spaced one from the other in a manner such as to provide a discharge gap between these two electrodes. The length of this gap is determined by the various parameters of the tube in accordance with the voltage at which the tube is designed to operate in the manner which is well known in the art.

In the embodiment shown in FIG. 1, an auxiliary or triggering electrode 23 is positioned in the discharge gap defined by the cathode 17 and the anode 13. The triggering electrode 23 is supported by leads 25 which are sealed through the envelope 10 and connected to a suitable control voltage source 24. One side of the control voltage source is connected to ground. In the specific embodiment shown, the electrode 23 consists of a block 22 of suitable semiconductor material such as silicon carbide. The block 22 is provided with P-N type junction and serves the purpose of emitting electrons into the discharge gap defined by the cathode 17 and the anode 13 when a reverse bias is applied. The reverse bias is applied to leads 25 by source 24. It is known that a P-N junction of semiconductive material exhibits the ability to emit high energy electrons upon the passing of an electrical current through the junction.

FIG. 2 is an enlarged view of the triggering electrode 23 shown in FIG. 1. The electrode 23 consists of a block 22 formed of a layer 43 of P-type material in contact with a base 35, of suitable material such as Inconel, and a layer 45 of N-type material adjacent the other sur face of the P-type layer, with an intermediate junction region 47. A contact member 41 is placed in contact with the N-type layer 45. By providing a potential of 7 to 40 volts from the source 24 such that contact 41 is positive with respect to base 35 and a collecting potential of volts to the anode 13 by means of the battery 39, an electron current was obtained which ranged from 10" to l() amperes. A more complete description of a manner in which the triggering electrode 23 may be formed may be found in a co-pending application Serial No. 787,011, filed January 15, .1959, entitled Electron Tube With a Cold Emissive Cathode, now US. Patent No. 3,105,166, by Wolfgang J. Choyke and Lyle A. Patrick and assigned to the same asignee. Other materials which may provide suitable electron sources other than silicon carbide include AlP, AuCs, GaP, ZnS, ZnSe, ZnO, NiO, A1 0 TiO and diamond.

The normal operation of the electronic device shown in FIG. 1 is as an electronic switching tube. Its operation is as follows. Under normal circumstances the voltage between the cathode 17 and anode 13 is insufficient to cause an arc discharge between these two electrodes. With no control voltage applied to the triggering electrode 23, no electrons will be emitted therefrom. However, When it is desired to have discharge and hence a switching within the tube, the application of a. control voltage of suitable size, for example 40 volts by the source 24, to the junction 47 of the triggering electrode 23 will cause the electrode 23 to emit high energy electrons at its junc tion area into the ionizable gas of the device. With the emission of a sulficient amount of electrons from the junction 47, an almost instantaneous ionization in the tube space will occur permitting an anode to cathode breakdown and hence a discharge within the tube at a lower than normal breakdown voltage. Once a cathode to anode discharge has been established the control volt age on the triggering electrode 23 may be removed. The discharge between the main cathode 17 and the anode 13 will then continue until such time as the anode to cathode potential drops to a value which will no longer sustain this discharge in the ionized space.

While the position of the triggering electrode 23 in this specific embodiment is shown to be in the discharge space between the cathode 17 and the anode 13, this position is not critical. As well as in the position shown, the electrode 23 may be placed adjacent to the cathode 17 at either side or in the region behind the cathode 17.

FIGS. 3 and 4 of the drawing illustrate a further modification of the invention. In this embodiment the triggering electrode 23 shown in FIG. 2 is incorporated into the main cathode instead of being a separate element within the tube. A cathode 57 is provided which is similar to that described with respect to FIG. 1 with the triggering electrode 23 having its base 35 secured to the cathode. The cathode 57 may serve as the base electrode 35 in some embodiments. The operation of the device, however, is substantially the same as that described with respect to FIG. 1. Here again, with no current flowing through the junction, the cathode to anode voltage in the main discharge gap is insufiicient to cause breakdown and it is not until suflicient charged particles are present within the gap that a discharge will form. It is also apparent that in this embodiment the control voltage is placed on the P-N type junction through the cathode lead 11 and through a lead 58.

Another possible modification of the cathode is to provide that the entire cathode be made of semiconductive material. In this instance, a small junction area of the P-type semiconductive material and the N-type semiconductive material will act as the triggering electron source and the rest of the semiconductive material constituting the whole of the cathode will act as the main cathode.

Since the P-N type junction has substantially instantaneous electron emission on the application of the suitable control voltage the gaseous discharge switching tube is capable of substantially instantaneous action.

While several embodiments of the invention have been shown and described in this application it will be apparent to those skilled in the art that various changes 4 and modifications may be made therein without departing from the essential features of the invention.

I claim as my invention:

1. A gaseous discharge device comprising an envelope, a plurality of lead in conductors extending through said envelope, a plurality of electrodes within said envelope, two of said electrodes defining a discharge gap, one of said electrodes incorporating a semiconductive P-N type junction for supplying electrons to said gap upon the application of a predetermined voltage potential to said junction.

2. A gaseous discharge device comprising a hermetically sealed envelope, a cathode and an anode within said envelope defininig a discharge gap therein, a triggering electrode within said envelope for supplying electrons to said discharge gap upon the application of a predetermined voltage potential to said triggering electrode, said triggering electrode comprising a body of semiconductive material and including a P-N type junction.

3. A cold cathode gas filled discharge device comprising a hermetically sealed envelope, a plurality of lead in conductors, two main electrodes defining a discharge gap, an auxiliary electrode consisting of a body of semiconductive material having a P-N type junction for supplying electrons to said discharge gap upon the application of a predetermined voltage potential to said junction.

4. A gaseous discharge tube comprising a hermetically sealed envelope containing an ionizable gas, a plurality of electrodes in said envelope defining at least one discharge gap, one of said electrodes having at least a portion of semiconductive material including a P-N type junction, means for providing an electrical field across said semiconductive junction to cause electrons to be emitted therefrom to initiate a discharge across said gap.

5. A gaseous discharge device comprising an envelope containing an ionizable gas; first and second elements within said envelope defining a discharge region; and a body of semiconductive material having therein a rectifying junction, and electrode means to establish a field within said body to provide an electron emission, one of said electrode means being formed integrally with said first element.

References Cited by the Examiner UNITED STATES PATENTS 2,592,683 4/52 Gray 315-56 X 3,105,166 9/63 Choyke 313-346 X 3,142,780 7/64 Rich 3l5166 X GEORGE N. WESTBY, Primary Examiner, 

1. A GASEOUS DISCHARGE DEVICE COMPRISING AN ENVELOPER, A PLURALITY OF LEAD IN CONDUCTORS EXTENDING THROUGH SAID ENVELOPE, A PLURALITY OF ELECTRODES WITHIN SAID ENVELOPE, TWO OF SAID ELECTRODES DEFINING A DISCHARGE GAP, ONE OF SAID ELECTRODES INCORPORATING A SEMICONDUCTIVE P-N TYPE JUNCTION FOR SUPPLYING ELECTRONS TO SAID GAP UPON THE APPLICATION OF A PREDETERMINED VOLTAGE POTENTIAL TO SAID JUNCTION. 